There was music included with the lyrics (see below) but it has been set to many other tunes since then. The one we are singing is an a cappella SATB version written by Robin John King, a Canadian composer.
There is no rose of such virtue
As is the rose that bare Jesu
Alleluia
For in this rose contained was
Heaven and earth in little space
Res miranda
By that rose we may well see
That he is God in persons three
Pari forma
The angels sung the shepherds to
Gloria in excelsis deo
Gaudeamus
Leave we all this worldly mirth
And follow we this joyful birth
Transeamus
Alleluia, res miranda
Pares forma, gaudeamus
Transeamus
Pari forma: Equal in form
Gloria in excelsis deo: Glory in the highest to God
Gaudeamus: Let us rejoice
Transeamus: Let us follow
I couldn't find the version we're singing online, but here is another one which is very good: